Device for therapeutic treatment of wounds

ABSTRACT

The invention concerns a device comprising a dressing provided with a layer ( 8 ) for absorbing the wound exudates and electric supply means ( 9 ) to circulate a current in said wound, through the dressing. The invention is characterized in that said layer ( 8 ) consists of a dry hydrophile substantially non-conductive layer at the time it is applied on the wound, the subsequent migration of the exudates into the thickness of said layer ( 8 ) controlling the activation of said electric supply means ( 9 ), concomitantly with the continuation of the process of exudate absorption by said layer ( 8 ).

The present invention relates to a device for therapeutic treatment ofwounds and, more particularly, to a device of this kind of the typeincluding a dressing provided with a layer for absorbing exudates fromthe wound and electric supply means to circulate a current in said woundthrough said dressing.

Many types of dressings have been designed to absorb the exudates from awound and to accelerate healing of the wound. One such dressing is asemi-occlusive and sterile adhesive dressing consisting of ahydrocolloid mass layer applied to a support consisting of apolyurethane film for local treatment of wounds such as leg ulcers orbed sores. The Chenôve, France company Laboratoires URGO manufactures adressing of this kind, which is marketed under the ALGOPLAQUE brand(registered trade mark). In contact with a wound, the hydrocolloidparticles dispersed in the layer absorb the exudates, swell and form, amoist gel encouraging healing of the wound without the newly formedtissues being damaged when the dressing is renewed.

Electrotherapy of wounds is a known technique for accelerating healing.The technique consists generaly in applying two electrodes to the skinof the patient and passing an electric current between the electrodes sothat the current enters a wound in the skin. The document EP-A-0 367 320describes a wound treatment system including a dressing consisting of anelectrically conductive compress, a return electrode and means forpassing an electric current between the compress and the returnelectrode. The compress includes an electrically conductive hydrophilegel layer which can contain up to 93-96% bound water and is renderedconductive by a metallic salt. The gel layer is applied to anelectrically conductive layer. An electric current flows in this layerand in the hydrophile gel layer and then in the wound before returningto the return electrode. The capacity of a gel of the above kind toabsorb exudates from the wound is limited by its initial moisturecontent.

The object of the present invention is to provide a device fortherapeutic treatment of wounds in which the capacity for absorption ofexudates from the wound is maximised, while being combined with anelectric treatment of the wound.

This object of the invention, along with others that will becomeapparent on reading the following description, is achieved with a devicefor therapeutic treatment of wounds of the type which includes adressing provided with a layer for absorbing exudates from the wound andelectric supply means to circulate a current in said wound, through saiddressing, which device is remarkable in that said layer consists of adry hydrophile layer which is substantially electrically non-conductiveat the time it is applied on the wound, subsequent migration of exudatesinto the thickness of said layer controlling the activation of saidelectric supply means.

Said initially dry hydrophile layer is therefore used withoutdeterioration of its capacity to absorb exudates. As will be shownlater, this initially non-conductive layer becomes conductive as itbecomes charged with exudates. It therefore becomes sufficientlyconductive at some stage to enable “electric” treatment of the wound.

In this regard, according to one feature of the device in accordancewith the present invention, said electric supply means include a circuitfor measuring the impedance of the hydrophile layer and means responsiveto said measurement falling below a predetermined threshold to commandthe activation of the electric supply means under nominal conditions.

Other features and advantages of the present invention will becomeapparent on reading the following description and examining theaccompanying drawings, in which:

FIGS. 1 and 2 are respectively a plan view and a sectional view of afirst embodiment of a dressing forming part of a device in accordancewith the invention and which includes both a “return” conductiveelectrode and an “active” electrode in contact with the wound,

FIG. 3 is a sectional view of a first embodiment of a device inaccordance with the invention, consisting of the dressing from FIGS. 1and 2 and electric supply means integrated into the dressing,

FIG. 4 shows a second embodiment of a dressing for a device inaccordance with the invention,

FIG. 5 shows another embodiment of a dressing for a device in accordancewith the invention in which only the “active” electrode is included inthe dressing, the “return” electrode being independent thereof,

FIG. 6 shows a second embodiment of the electric supply means of adevice in accordance with the invention, designed to be associated withthe dressing from FIG. 5,

FIG. 7 is a functional block diagram of electric supply means of adevice in accordance with the invention, and

FIGS. 8 and 9 are graphs respectively showing the process of chargingwith exudates and the evolution of the impedance of a hydrophile layerforming part of a dressing in accordance with the invention.

FIGS. 1 and 2 of the accompanying drawings show that the firstembodiment of a dressing forming part of a device in accordance with theinvention is substantially flat in shape and rectangular, with a sidelength of a few centimetres, for example, so as to have a surface areasubstantially twice that of a wound to be covered.

The dressing includes, on a flexible support 1, two electrodes 2 and 3separated by a strip 4 of insulative material. The electrodes 2 and 3are in electric contact with respective electrically conductive materialstuds 5, 6 which pass through the support 1 and are flush with itsoutside surface.

One of the electrodes, for example the electrode 2, referred to as thereturn electrode, is covered with a conductive layer 7 constituting aninterface with the skin of the patient. The other electrode 3, referredto as the active electrode, and which is in contact with the wound, iscovered, in accordance with the invention, with a dry hydrophile layer 8which is not electrically conductive in the dry state.

Electric supply means, described in more detail hereinafter withreference to FIG. 7, are connected to the studs 5, 6 to establish andcontrol an electric current flowing between the two electrodes when thedressing is applied to the skin of a patient, the dry hydrophile layer 8being pressed against a wound to be healed and the conductive layer 7being applied to an area of the skin adjacent the wound.

For fixing the dressing in this position, adhesive means (not shown) canbe provided on the dressing, for example on the support 1, at theperiphery thereof.

The electric supply means can be physically separate from the dressingand connected to the studs 5, 6 by electric wires. They can also beintegrated into the dressing and discarded with it. FIG. 3 shows suchmeans 9 including an autonomous electric energy source such as a battery10 and diverse discrete or integrated electronic components 11. Themeans 9 are fixed to the flexible support 1 above the studs 5, 6. As analternative to this, these means can be received removably on thedressing, thanks to mechanical assembly means such as press-studs,grooves, meshes, “Velcro” (registered trademark), etc so that they canbe removed after treatment and re-used on a new dressing.

As soon as the dressing is fixed over the wound, the dry hydrophilelayer 8 begins to be charged with exudates from the wound. In vitrotests have been carried out to study this process, using cells filledwith physiological serum and closed by a sample of a layer 8 consistingof a 1 mm thick hydrocolloid mass in contact with the serum, the lattersimulating the exudates from a wound. The kinetics of charging of thephysiological serum layer were established by measuring cumulatively thequantity of serum absorbed by the layer between two consecutivemeasurements. The FIG. 8 graph represents the average kinetics ofcharging of the cells used.

The evolution of the resistance of the layer was measured byestablishing an electric current in the cell, through the layer, atregular time intervals, and measuring the resulting voltage, the currentdensity established during the measurements being 0.11 mA/cm². The FIG.9 graph shows the evolution in time of the average of the resistancescalculated in this way for the cells used. The graph shows that duringthe first few hours it was not possible to evaluate the conductivitybecause the layer 8 remained substantially non-conductive in thisperiod.

The sudden appearance of conductivity in the layer 8, as shown in FIG. 9and occurring after 6 to 8 hours, can be explained by regularprogressive migration of the serum, and therefore of the exudates from awound, which are rich in mineral salts and therefore highly conductive,from the face of the layer 8 which is in contact with the wound to theother face of that layer, which is in contact with the electrode 3. Thusthe resistance of the layer 8 remains high for as long as the exudateshave not reached the other face. It drops to a much lower value as soonas the exudates reach that other face. The layer 8 is then conductivethroughout its thickness and an electric current can be passed throughit, in the case of a treatment seeking to accelerate healing of thewound.

Accordingly, in accordance with the invention, the beneficial effects ofabsorbing exudates from the wound in a hydrophile layer are combinedwith this electric treatment, without sacrificing in any way theabsorption capacity of the hydrophile layer used which, in the priorart, had to be rendered initially conductive by a charge of water andmineral salts, to the detriment of its total capacity to absorbexudates.

In this regard, the FIG. 8 graph shows that after about 7 hours (420minutes) the hydrophile layer 8 was charged with approximately 1000 g/m²of exudates to reach a conductivity compatible with electric treatmentof the wound, such charging being advantageously substituted for thecharging with saline solution used in the prior art to impart thisconductivity to it.

In the present invention, the electric treatment is delayed for a fewhours, which is of no account compared to the time for a wound to heal,which is ordinarily in the order of several days to several weeks.Furthermore, the absorption of the exudates by the hydrophile layerbegins as soon as the dressing is applied, before electric treatment ofthe wound.

The layer 8 of the dressing in accordance with the present invention canbe made from many dry hydrophile products, alone or in combination, forexample in the form of fibres, dispersed particles or foam. Thethickness of the layer is advantageously from 200 to 2000 μm, preferablyfrom 300 to 1000 μm. If the layer is not inherently self-adhesive, thedressing can be provided with adhesive means for fixing the dressing tothe skin of the patient, as mentioned above.

The dry hydrophile layer can be made from any material or dry hydrophileabsorbing substances used in the manufacture of dressings for treatingexuding wounds.

Thus it can be in the form of absorbent foams, in particular hydrophilepolyurethane foams as used in so-called hydrocellular dressings, in theform of fibres based on absorbent materials, for example alginatefibres, such as sodium or calcium alginate fibres, or cellulosederivative fibres, in the form of non-woven compresses, in the form offreeze-dried gels and in the form of hydrocolloidal substances such asgels or hydrocolloidal masses such as those used in so-calledhydrocolloid dressings.

In the context of the present invention, hydrocolloid masses arepreferred for the dry hydrophile layer.

These hydrocolloid masses are formed principally of an adhesiveelastomer chosen from polymers such as polyisobutenes or sequencedpoly(styrene-olefin-styrene) copolymers such as, for example,poly(styrene-isoprene-styrene) or poly(styrene-ethylenebutylene-styrene), associated or not with so-called sticky “tackifying”resins, plasticisers, etc and one or more hydrocolloids. Thehydrocolloids usable in the masses referred to here are substancesroutinely used by the skilled person, known for their ability to absorbhydrophile liquids, in particular water and exudates, and to transportthem rapidly. Appropriate hydrocolloids include, for example, polyvinylalcohol, gelatine, pectin, natural vegetable gums such as carob gum,Karaya gum, guar gum, gum arabic, etc, cellulose derivatives such ashydroxyethylcelluloses, hydroxypropylcelluloses, carboxymethylcellulosesand their alkaline metal salts, such as their sodium or calcium salts.These hydrocolloids can be used alone or in combination.

Such masses are described in patent applications EP-A-130 061, EP-092999 and WO-98/10801 and in U.S. Pat. No. 3,972,328.

The flexible support 1 can be cut out from a film of plastics materialsuch as polyethylene, polyurethane, polyester or a polyimide. Theelectrodes 2 and 3 can be formed by screen printing a conductive inkonto this film. An Ag/AgCl type ink can be used to form so-called“sacrificial” electrodes adapted to prevent electrolysis of the waterand therefore to maintain the pH of the exudates in the layer 8 of thewound constant, if required.

The electrodes 2, 3 can also be of metal, for example copper, zinc,silver or platinum, or of carbon or a conductive polymer.

The strip 4 is made from a material adapted to constitute a barrier toelectricity and to moisture, such as a plastics material foam.

The “return” electrode 2 is covered with a layer 7 of a materialassuring good contact with the skin and return flow of the current. Thislayer can be of polyoxyethylene or polyethylene-glycol, for example,cross-linked and containing sufficient water and salts to be a goodconductor of electricity.

The structure of one embodiment of the electric supply means of thedevice in accordance with the invention will now be described withreference to FIG. 7. When these means are integrated into the dressing,as mentioned above, they take the form of an electronic circuit whosecomponents (battery, discrete or integrated components) are mounted onconductive tracks formed on the support 1 by any technique known in theart: refusion, adhesive bonding, wave soldering, etc. They can also beremovable and re-usable, or even entirely separate from the dressing, towhich they are then connected by appropriate electrical connections.

In the embodiment of this circuit shown diagrammatically in FIG. 7, thecircuit essentially includes one or more electric batteries 10, forexample of the “button” cell type, adapted to provide an autonomouselectric supply of the circuit, of low weight and with overalldimensions compatible with the portable nature of the dressing on whichit is mounted, at least in the case of the embodiment of the dressingshown in FIG. 3. The battery 10 feeds a switch-mode power supply 12which increases the voltage at the terminals of the battery to supply acurrent generator 13 of any suitable type, for example the Howllandtype. This generator feeds current into the electrodes 2, 3 under thecontrol of a sub-circuit 14.

According to the present invention, when the treatment begins the dryhydrophile layer 8 has substantially infinite impedance because it hasnot been hydrated by exudates from the wound. For a suitable electriccurrent to flow, for example a current in the order of 1 mA, it isnecessary to wait until hydration of the layer has reduced its impedanceto a sufficiently low value, for example in the order of a few kΩ.

Thus at the beginning of the treatment, the sub-circuit 14 initiallycontrols a generator 13 in such a way that it passes, or attempts topass, a low current between the electrodes, sufficient only to enablemeasurement of the impedance of the layer 8 by the sub-circuit 15. Thiscircuit compares the measured impedance to a predetermined threshold,enabling detection of the sudden drop in impedance shown in the FIG. 9graph. When that threshold is reached, after 6 to 8 hours, for example,the sub-circuit 14 switches the output current of the generator 13 to apredetermined nominal current, corresponding to saturation of thegenerator, for example. The electric treatment of the wound can thenbegin.

It can develop in time in accordance with a predetermined program,alternating time intervals ΔT_(ON) in which current flows in the woundand time intervals ΔT_(OFF) in which no current flows in the wound. Thesuccession of time intervals can be programmed and controlled by amicrocontroller 16 and by time counters 17, 18 incorporated in themicrocontroller, as shown here, or external thereto.

It is now clear that the invention achieves the stated objects, namelyto provide a device for treating a wound by electrotherapy including alayer for absorbing exudates from the wound whose capacity to absorb theexudates is not compromised by the necessity to render the layerelectrically conductive. Note that, in the embodiment of the deviceshown in FIG. 3, the device has a particularly compact form, similar tothat of a conventional dressing, the electrotherapy treatment meansbeing integrated into the dressing.

Of course, the invention is not limited to the embodiments shown inFIGS. 1 to 3. Thus the electrodes of the device, which are adjacent inthe embodiment of FIGS. 1 to 3, could also be concentric, as shown inFIG. 4, in which reference numbers identical to the reference numbersused in FIG. 1 represent identical or similar elements or units. The dryhydrophile layer 8 is then placed at the centre and the conductive layer7 placed on the return electrode 2 has a closed contour, this layerbeing separated from the layer 8 by an insulative strip 4, which alsohas a closed contour.

The dressing can include only the active electrode (3), as in theembodiment of the device in accordance with the invention shown in FIG.5. In this case, the return electrode (2) is formed of a support (1′)separate from a support (1) of the active electrode (2) of the dressingand is totally independent of the dressing. For the electric supply ofthe dressing it is then necessary to provide the means shown in FIG. 6including a circuit 9 of the type described in relation to thedescription of the embodiment of FIGS. 1 to 3 and flexible electriclines such as the lines 20, 21, 22 for connecting the poles 23, 24 ofthe circuit to the contact studs 5, 6 of the electrodes of the FIG. 5embodiment, via clamps 25, 26, 27, 28, 29. Note that the clamps 28, 29are used to connect two return electrodes to the circuit 9. The numberof return electrodes, installed at a distance from the electrode whichis applied to the wound to be treated, can obviously be varied to obtaina more regular distribution of the therapeutic current in the wound.

What is claimed is:
 1. A device for therapeutic treatment of wounds,said device comprising: a dressing for contact with a wound and providedwith a dry hydrophilic layer for absorbing exudates from the wound, saidlayer, upon said contact, being free of sufficient hydrating materialfor electrical conductivity; and electric supply means for circulating acurrent in said wound through said dressing, activation of said electricsupply means being controlled by subsequent migration of exudates intosaid layer concomitantly with continuation of a process of exudateabsorption by said layer.
 2. The device according to claim 1, whereinsaid dry hydrophilic layer is chosen from the group consisting ofpolyurethane foams, non-woven compresses, hydrocolloid masses and gels,fibres of alginates and cellulose derivatives in the form offreeze-dried gels.
 3. The device according to claim 1, wherein saiddressing includes two electrodes formed on a common plane support, oneof said electrodes being covered with said dry hydrophilic layer, saidsupply means being connected to said electrodes to cause an electriccurrent to flow between them.
 4. The device according to claim 3,wherein said electrodes are adjacent.
 5. The device according to claim3, wherein said electrodes are concentric.
 6. The device according toclaim 1, wherein said dressing includes an active electrode formed on aplane support, said active electrode being covered with said dryhydrophilic layer, and said device includes at least one returnelectrode formed on a plane support separate from that of said activeelectrode, said supply means being connected to said active and returnelectrodes to cause an electric current to flow between them.
 7. Thedevice according to claim 1, wherein said dressing includes adhesivemeans enabling said dressing to be fixed to the skin of a patient. 8.The device according to claim 1, wherein said electric supply meansinclude means for controlling the output current.
 9. The deviceaccording to claim 8, wherein said electric supply means include meansfor controlling the output current in time.
 10. The device according toclaim 8, wherein said supply means include a circuit for measuring theimpedance of the hydrophilic layer and means responsive to saidmeasurement falling below a predetermined threshold to activate thesupply means under nominal conditions.
 11. The device according to claim1, wherein said supply means are integrated into the dressing.
 12. Thedevice according to claim 1, wherein said device includes means forremovably mounting said supply means on the dressing.
 13. The deviceaccording to claim 1, wherein said dry hydrophilic layer is free of allhydrating material upon contact with a wound.
 14. A dressing for use ina device for therapeutic treatment of wounds and for contacting a woundwhen in use, said dressing comprising: a dry hydrophilic layer forabsorbing exudates from a wound, said layer being free of sufficienthydrating material for electrical conductivity when initially put intouse; and an electrode formed on a planar support and covered with saiddry hydrophilic layer.
 15. The dressing according to claim 14, whereinsaid dry hydrophilic layer is free of all hydrating material wheninitially put into use.
 16. The dressing according to claim 14, whereinsaid layer is charged through absorption of wound exudates and as aresult becomes electrically conductive following a period of use. 17.The dressing according to claim 14, wherein said dry hydrophilic layeris a hydrocolloid mass.
 18. A device for therapeutic treatment ofwounds, said device comprising: a dressing for absorbing exudates from awound when in use, said dressing including a dry hydrophilic layerwhich, when initially put into use, is free of sufficient hydratingmaterial to effect electrical conductivity in said layer; and electroniccircuitry for circulating a current in said wound through said dressing,activation of said electronic circuitry being dependent upon exudateabsorption by said layer.
 19. The device according to claim 18, whereinsaid dry hydrophilic layer is free of all hydrating material wheninitially put into use.
 20. The device according to claim 18, whereinsaid layer becomes electrically conductive as a result of exudateabsorption over a period of use.